This invention relates generally to improvements in infusion pumps of the type used for controlled delivery of medication to a patient. More specifically, this invention relates to an improved occlusion detector for use in a medication infusion pump, to provide an early alarm of medication nondelivery due to an occlusion along the medication delivery flow path or other pump drive system failure.
Infusion pump devices and systems are relatively well-known in the medical arts, for use in delivering or dispensing a prescribed medication such as insulin to a patient. In one form, such devices comprise a relatively compact pump housing adapted to receive a syringe carrying a prescribed medication for administration to a patient through infusion tubing and an associated catheter or the like. The infusion pump includes a small stepping drive motor having an output connected via a lead screw assembly for motor-driven advancement of a syringe piston plunger to administer the medication to the patient. Programmable control means are normally provided for operating the drive motor at periodic intervals to obtain a closely controlled and accurate delivery of the medication over an extended time period. Such infusion pumps are utilized to administer insulin and other medications, with an exemplary pump construction being shown and described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903, which are incorporated by reference herein.
Infusion pumps of the general type described above have provided significant advantages and benefits with respect to accurate delivery of medication over an extended time period. The infusion pump is often designed to be extremely compact and may thus be adapted to be carried by the patient, for example, by means of a belt clip or the like. As a result, important medication can be administered with precision and in an automated manner, without significant restriction on the patient's mobility or life-style.
In the past, medication infusion pumps have included alarm systems designed to detect and indicate pump malfunction and/or nondelivery of the medication to the patient as a result of an occluded delivery line. Such alarm systems have typically used a high pressure limit switch for activating an alarm when the force applied to the syringe piston plunger reaches a predetermined upper limit indicative of an occluded medication delivery line. In U.S. Pat. No. 4,562,751, the high pressure switch is positioned at one end of a rotatable lead screw, wherein the mechanical reaction force or backlash between the syringe plunger and the pressure switch is proportional to the pressure applied to the medication as a result of attempted advancement of the syringe plunger. In actual practice, however, such high pressure limit switches have not provided the desired early warning of an occlusion, but instead have required multiple consecutive nondelivered doses before the pressure will rise to a level sufficient to activate the high pressure switch. For many patients, it may take several hours for the occurrence of several consecutive doses, whereby an occlusion may go undetected for an undesirably long period of time. This problem is especially significant when the patient is a child, and wherein each dose comprises a relatively small volume of the medication.
There exists, therefore, a significant need for further improvements in medication infusion pumps particularly with respect to improved and rapid response occlusion detection for providing an early warning of an occlusion or other pump drive system failure. The present invention fulfills this need and provides further related advantages.